Method and apparatus for determining biofouling of a membrane

Abstract

A method of determining a state of biofouling of a membrane is provided. The membrane is contained within a flow cell and the flow cell has an outer surface coupled to a tranducer, The method comprises introducing inorganic particles into the flow cell such that the inorganic particles form a part of a top surface of a foulant layer on the membrane. The transducer then emits acoustic waves towards the membrane and an acoustic signature of reflected sound waves are detected. A state of biofouling of the membrane is determined based on the detected acoustic signature. A method and an apparatus are also provided for determining a state of biofouling in commercial membrane modules such as spiral wounded membrane modules.

The invention claimed is: 
     
       1. A method of determining a state of biofouling of a membrane contained within a flow cell, the flow cell having at least an outer surface coupled to one or more acoustic transducers, the method comprising the following steps:
 introducing inorganic particles into the flow cell such that the inorganic particles form at least a part of a top surface of a foulant layer on the membrane; 
 emitting acoustic waves towards the membrane using the one or more transducers; 
 detecting an acoustic signature of reflected sound waves, the acoustic signature comprising a profile of reflected sound waves from the top surface and a profile of reflected waves from the membrane; and 
 determining, based on the detected acoustic signature, a state of biofouling of the membrane. 
 
     
     
       2. The method of  claim 1 , wherein the membrane is a flat sheet membrane. 
     
     
       3. The method of  claim 1 , wherein the acoustic signature further comprises a profile of reflected sound waves from a reference point. 
     
     
       4. The method of  claim 3 , wherein the step of determining comprises comparing the profile of reflected sound waves from the top surface and the profile of reflected sound waves from the membrane against the profile of reflected sound wave from the reference point. 
     
     
       5. The method of  claim 1 , wherein the step of determining further comprises analysing the acoustic signature using ultrasonic time domain reflectometry. 
     
     
       6. The method of  claim 1 , wherein the state of biofouling comprises at least one of: a thickness of the foulant layer, the rate at which biofouling occurs, and the amount of membrane compaction. 
     
     
       7. The method of  claim 1 , wherein the inorganic particles comprise particles capable of enhancing an acoustic impedance difference between the foulant layer and the membrane. 
     
     
       8. The method of  claim 1 , wherein the inorganic particles comprise particles capable of enhancing an acoustic impedance difference between the foulant layer and the feed solution. 
     
     
       9. The method of  claim 1 , wherein the inorganic particles comprise at least one of: silica particles, nanoparticles, glass beads, and a colloidal insoluble compound. 
     
     
       10. The method of  claim 1 , wherein the step of introducing inorganic particles comprises one of: intermittently injecting, partially injecting and continuously injecting the inorganic particles. 
     
     
       11. The method of  claim 1 , wherein the acoustic transducer is a focused transducer. 
     
     
       12. The method of  claim 1 , further comprising a step of removing the inorganic particles from the flow cell. 
     
     
       13. The method of  claim 1 , comprising repeating the method with the step of  claim 12 . 
     
     
       14. A method of determining a state of biofouling of a first membrane in a membrane module, the method comprising the steps of:
 providing an ancillary flow cell comprising a second membrane in parallel with the membrane module; 
 diverting part of a feed stream for the membrane module as a side stream into the ancillary flow cell; 
 introducing inorganic particles into the ancillary flow cell such that the inorganic particles form at least a part of a top surface of a foulant layer formed on the second membrane due to the side stream; 
 emitting acoustic waves towards the second membrane using at least one transducer; 
 detecting an acoustic signature of reflected acoustic waves, the acoustic signature comprising a profile of reflected sound waves from the top surface and a profile of reflected sound waves from the second membrane; 
 determining, based on the detected acoustic signature, a state of biofouling of the second membrane; and 
 configuring the ancillary flow cell relative to the membrane module such that a state of biofouling of the ancillary flow cell is indicative of a state of biofouling of the first membrane in the membrane module. 
 
     
     
       15. The method of  claim 14 , wherein the second membrane is a flat sheet membrane. 
     
     
       16. The method of  claim 14 , wherein the acoustic signature further comprises a profile of reflected sound waves from a reference point. 
     
     
       17. The method of  claim 14 , wherein the step of determining comprises comparing the profile of reflected sound waves from the top surface and the profile of reflected sound waves from the membrane against the profile of reflected sound wave from the reference point. 
     
     
       18. The method of  claim 14 , wherein the step of determining further comprises analysing the acoustic signature using ultrasonic time domain reflectometry. 
     
     
       19. The method of  claim 14 , wherein the state of biofouling comprises at least one of: a thickness of the foulant layer, the rate at which biofouling occurs, and the amount of membrane compaction. 
     
     
       20. The method of  claim 14 , wherein the inorganic particles comprise particles capable of enhancing an acoustic impedance difference between the foulant layer and the second membrane. 
     
     
       21. The method of  claim 14 , wherein the membrane module is one of: a spiral wound module and a hollow fiber membrane module. 
     
     
       22. The method of  claim 14 , wherein the ancillary flow cell is configured to foul earlier than the membrane module. 
     
     
       23. The method of  claim 14 , further comprising removing the inorganic particles from the ancillary flow cell. 
     
     
       24. An apparatus for determining a state of biofouling of a first membrane in a membrane module, the apparatus comprising:
 an ancillary flow cell configured to receive part of a feed stream diverted from the membrane module, the ancillary flow cell comprising a second membrane provided in a compartment defined between a top plate and a bottom plate; 
 inorganic particles configured to be introduced into the ancillary flow cell to form at least a part of a top surface of a foulant layer formed on the second membrane; 
 at least one transducer provided on at least one of: the top plate and the bottom plate, the at least one transducer configured to emit acoustic waves towards the second membrane and to receive reflected waves from the top surface and reflected waves from the second membrane; and 
 an analysis module configured to perform acoustic reflectometry measurements and to determine a state of biofouling of the ancillary flow cell based on acoustic signatures of the reflected waves from the top surface and reflected waves from the second membrane; 
 such that a state of biofouling of the ancillary flow cell is indicative of a state of biofouling of the first membrane in the membrane module. 
 
     
     
       25. The apparatus of  claim 24 , wherein the second membrane is a flat sheet membrane. 
     
     
       26. The apparatus of  claim 24 , wherein the state of biofouling comprises at least one of: a thickness of the foulant layer, the rate at which biofouling occurs, and the amount of membrane compaction. 
     
     
       27. The apparatus of  claim 24 , wherein the inorganic particles comprise particles capable of enhancing an acoustic impedance difference between the foulant layer and the second membrane. 
     
     
       28. The apparatus of  claim 24 , wherein the ancillary flow cell is configured to foul earlier than the membrane module.